What on Earth Made This?
Answer Key

Yes. Millions of years of surface erosion shaped the spectacular stone
sculptures of Arches National Park in eastern Utah. Delicate Arch, perched
precariously on the edge of a canyon, is just one of 1,500 arches in the park,
with spans reaching up to 300 feet. Most of the arches likely began as solid
walls, or fins. Wind and water dug holes in the fins' porous
sandstone—holes that were further enlarged by rockfalls and weathering.
Many structures collapsed, but some with the right hardness and balance
survived.

2. (c) slow-cooling lava

Correct. The Devil's Postpile was indeed made by a fiery force—a
massive lava flow that scalded the land 100,000 years ago. When the thick
volcanic flow slowly cooled, it began to shrink. Cracks formed, first at the
surface and then propagating downward, fracturing the solidified lava into
columns. While some of the columns have three, four, five, or seven sides, most
are hexagonal—the pattern that allows for the most shrinkage with the
fewest cracks. Similar six-sided columns exist elsewhere, including the
Palisades Sill north of New York City and the Giant's Causeway in Northern
Ireland.

3. (b) a meteorite

Yup. Its actual name is a giveaway—The Barringer Meterorite Crater, or
simply Meteor Crater. If you picked "an explosion of volcanic steam," don't
feel bad. At the turn of the 20th century, many scientists thought the same. A
mining engineer named Daniel Barringer, though, was convinced that iron
fragments around the crater were evidence of a meteor impact, and he assumed
the meteor's iron remnants would be a mining bonanza. He was right about the
impact, but wrong to launch a costly mining venture. Most of the meteor, which
likely measured 150 feet across and struck the Earth at 40,000 miles per hour,
vaporized on impact 50,000 years ago.

4. (c) the environment of an ancient salty lagoon

That's right. Roughly 155 million years ago, a warm shallow sea covered what is
now southern Germany. Coral reefs rose to cordon off the sea into isolated lagoons,
which became increasingly salty and devoid of oxygen. Most creatures that fell
into the lagoons couldn't survive long, and when they sank to the bottom, they
were quickly buried in fine-grained carbonate mud. The low oxygen level and
lack of strong currents in the lagoons delayed the decay of even delicate
organic materials like feathers until long after burial. When the encasing mud
turned to stone, the intricate details of the skeleton were essentially
cast in stone.

5. a) underwater vortexes

Indeed. Scientists reconstructing the events of cataclysmic Ice Age floods
suspect that powerful kolks—vortexes akin to underwater
tornadoes—gouged out the potholes. Some kolks likely were generated when
two distinct flows of raging water, travelling at slightly different speeds,
met and sheared past each other. Other kolks could have formed when a deep and
fast flow passed over a large outcrop of rock. The whirling kolks acted like
monstrous sledgehammers, pounding out huge chunks of bedrock that were then
swept away in the flood.

6. (b) minerals that precipitated around objects

Good pick. Each "pumpkin" is technically known as a concretion—a compact
mass of minerals that forms around a core object such as a shell or piece of
bone. These pumpkins formed underground within a bed of Diablo sandstone. Over
many centuries, rainwater dissolved so-called "cementing" minerals at the
surface and carried them downward. The minerals latched onto buried organic
objects, encasing them in newly hardened sandstone. Layer upon layer, the
pumpkins grew. They eventually made it to the surface, as wind and water eroded
the softer sandstone in which they were buried.

7. (a) the same forces that carve caves

Yes. And the towers are themselves riddled with caves. Limestone is a porous
sedimentary rock created ages ago from the remains of marine life. Weak acids
that naturally occur in groundwater dissolve the limestone and, together with
erosion and rockfalls, carve caves, karst valleys, and a host of other
fantastic landforms. Dramatic karst towers form in tropical regions like Guilin
when thick limestone dissolves rapidly. The columns and spires are left behind
after surrounding sections of limestone collapse or erode away.

8. (c) glaciers and ice wedging

Correct. Roughly 12,000 years ago, a retreating ice sheet sheered the sides of
Profile Mountain. After the glaciers melted, ice continued to play a role in
chiseling the features of the face: water seeped into cracks in the granite and
then froze, expanding by about 9 percent. This so-called ice wedging helped cut
the five distinct ledges that made the Old Man's forehead, nose, mouth, and
chin. Eventually, such ice wedging, along with changes in the granite called
chemical weathering, led to the Old Man's collapse. He remains the state symbol
for New Hampshire, but his passing makes clear the ephemeral nature of every
structure on Earth—even those "carved in stone."